Low back pain afflicts more than 10 million people in the United States annually. It impacts the individual sufferer's life physically, emotionally and financially, restricting his or her activities and often leading to depression and absenteeism from work. As a nation, the United States spends more than $50 billion dollars in direct and indirect medical expenses related to back pain, making it one of the leading healthcare expenditures overall.
The intervertebral disc consists of the anulus fibrosus, nucleus pulposus, and the endplates of the superior and inferior vertebral bodies. The anulus and endplates contain the nucleus as the disc is pressurized during normal activities. The posterior anulus is thinner in cross-section than the anterior anulus and is correspondingly the site most frequently affected by injury.
Deterioration of the structure of the intervertebral disc is one of the leading causes of low back pain. The intervertebral disc is formed from a tough, outer anulus fibrosus surrounding a softer, gelatinous nucleus pulposus. The anular fibers attach securely to the endplates of the vertebral bodies superiorly and inferiorly, trapping the nucleus and creating an isobaric environment. As load is applied through the spinal column, pressure within the nucleus increases and is distributed across the vertebral endplates and anulus. These structures flex and strain until the spinal load is equilibrated by intradiscal pressure allowing the disc to act as a “shock absorber”, Lack of significant vascularity in the anulus and nucleus limits their healing potential.
Small nerve endings penetrate the outer anulus. As a person ages, rents in the inner or central layers of the anulus can create focal regions of high pressure in the outer anulus that mechanically stimulates these nerve endings resulting in pain. There is also an increasing body of evidence suggesting an inflammatory response in and around nerves within the anulus and within the epidural space behind the disc induced by chemicals within the nucleus, vertebral endplates, and vertebral bodies. Passage of these chemicals through the anulus can also occur because of damage to the anulus through physical trauma, progressive aging, or degenerative disc disease. Under normal loading, portions of the nucleus or its degenerative byproducts may be forced into and through rents in the anulus, such chemicals are thought to be transported into proximity with these sensitive nerves resulting in inflammation and pain.
Therapeutic methods involving decreasing the temperature of the body or tissues thereof have a long history in medicine. Cold has been used successfully to bring about localized tissue necrosis, for cryoblation of tissue, as an anesthetic, and as a technique for inducing angiogenesis as a part of an overall healing response to the cold injury. Cryotherapy can be defined as the therapeutic use of cold and is not limited by any particular range of temperatures. Cryosurgery or cryocautery is usually more narrowly defined not merely as the use of cold in surgical applications but as the technique of exposing tissue to extreme cold in order to produce well demarcated areas of cell injury and destruction. Cryosurgical temperatures are typically below −20° C. On the other hand, hypothermia therapy involves a technique of lowering body or tissues thereof below body temperature, usually between 26° C.-32.5° C., Cryosurgery is distinguishable from the other two methods in that tissue is cut or ablated or otherwise destroyed with precision whereas cyrotherapy and hypothermia therapy techniques utilize cold or extreme cold to improve the health of tissue through stimulation. Accordingly, for purposes of this disclosure, hypothermia therapy includes cryotherapy or the therapeutic use of cold and extremely cold temperatures well below normal body temperature. Also, to the extent that related instrumentation such as hypothermia needles, cryogenic catheters, and cryoprobes (flexible or rigid) can be used to apply cryoenergy or cool tissue to a broad range of temperatures below normal body temperature, use of a specific type of instrument in a method of the invention disclosed herein does not necessarily imply a certain range of therapeutic temperatures. For instance, cryoprobes and cryocatheters may be used interchangeably according to various embodiments of the present invention.